Air-ground detection system for semi-levered landing gear

ABSTRACT

A method and apparatus for air-ground detection. A truck beam of a semi-levered landing gear is mounted on a pivot pin. The truck beam is configured to rotate about the pivot pin between a toes down position and a toes up position. A positioning mechanism is connected to a locking mechanism that secures an angle of the truck beam in the toes up position. The locking mechanism is secured in a steady state and configured to change from the steady state to a locked state in response to an initial ground contact. A sensor is connected to the locking mechanism. The sensor is configured to detect a change from the steady state to the locked state.

BACKGROUND INFORMATION

1. Field

The present disclosure relates generally to landing gear and, inparticular, to semi-levered landing gear. Still more particularly, thepresent disclosure relates to an air-ground detection system forsemi-levered landing gear.

2. Background

Many airplanes include landing gear to facilitate takeoff, landing, andtaxi. The landing gear of some aircraft includes a shock absorber thatis pivotally connected to a truck beam at a distal or lower end thereof.The truck beam typically includes two or more axles upon which tires aremounted. In this regard, the truck beam may include a forward axlepositioned forward of the shock absorber and an aft axle positioned aftof the shock absorber. Wheels may be mounted on an axle in tandem pairs.

During landing in conventional airplanes, a truck tilt actuator mayposition tandem axle wheels in a toes up position or a toes downposition. The toes up position is a configuration in which the forwardwheels on the main landing gear are at a higher position than that ofthe rear wheels on the main landing gear. A toes down position is aconfiguration in which the forward wheels are at a lower position thanthat of the rear wheels on the main landing gear. Upon landing, theforce of touchdown causes the truck beam to rotate so that front andrear wheels are aligned substantially horizontally on the ground.

Air-ground detection systems determine when the landing gear wheel orwheels touch the ground during landing for spoiler deployment, brakeactivation, and/or other desirable functions. Conventional aircraft mayutilize air-ground detection sensors which detect rotation of the truckbeam and use this rotation to determine when landing gear wheels makecontact with the ground.

However, this type of air-ground sensing system may not be usable with,or appropriate for, all types of landing gear. Accordingly, it would beadvantageous to have a method and apparatus which takes into account oneor more of the issues discussed above, as well as possibly other issues.

SUMMARY

One advantageous embodiment provides an air-ground detection system. Atruck beam of a semi-levered landing gear is mounted on a pivot pin. Thetruck beam is configured to rotate about the pivot pin between a toesdown position and a toes up position. A positioning mechanism isconnected to a locking mechanism that secures an angle of the truck beamin the toes up position. The locking mechanism is secured in a steadystate and configured to change from the steady state to a locked statein response to initial ground contact. A sensor is connected to thelocking mechanism. The sensor is configured to detect a change from thesteady state to the locked state.

In another advantageous embodiment, a method is provided for air-grounddetection in a semi-levered landing gear. An orientation of a number oflinks of a semi-levered linkage assembly is monitored. An initial groundcontact position of the semi-levered landing gear is indicated inresponse to detecting the semi-levered linkage assembly changing from asteady state to a locked state.

In yet another advantageous embodiment, a vehicle includes a fuselage, awing connected to the fuselage, and a semi-levered landing gearassembly. The semi-levered landing gear assembly is connected to atleast one of the fuselage, the wing, and an actuator. The semi-leveredlanding gear assembly comprises a truck beam connected to a shockabsorber and mounted on a pivot pin enabling the truck beam to rotatefrom a toes up position to a toes down position. A number of positioningsprings are connected to a semi-levered linkage assembly. The number ofpositioning springs includes a tension spring. A compression springexerts force in opposition to secure the semi-levered linkage assemblyin a steady state. The semi-levered linkage assembly is connected to thetruck beam and the shock absorber in the steady state prior to initialground contact during a landing procedure. A number of links within thesemi-levered linkage assembly is configured to change orientation fromthe steady state to a locked state in response to an initial groundcontact of a number of aft wheels with a ground. A sensor connected tothe semi-levered linkage assembly detects a change in the orientation ofthe number of links from the steady state to the locked state. Thesensor is configured to generate a signal indicating an occurrence ofthe initial ground contact in response to detecting the change in theorientation from the steady state to the locked state.

The features, functions, and advantages can be achieved independently invarious advantageous embodiments of the present disclosure or may becombined in yet other advantageous embodiments in which further detailscan be seen with reference to the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the advantageousembodiments are set forth in the appended claims. The advantageousembodiments, however, as well as a preferred mode of use, furtherobjectives and advantages thereof, will best be understood by referenceto the following detailed description of an advantageous embodiment ofthe present disclosure when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is an illustration of an aircraft manufacturing and servicemethod in accordance with an advantageous embodiment;

FIG. 2 is an illustration of an aircraft in which an advantageousembodiment may be implemented;

FIG. 3 is an illustration of a block diagram of an air-ground detectionsystem in which an advantageous embodiment may be implemented;

FIG. 4 is an illustration of a block diagram of a vehicle in which anadvantageous embodiment may be implemented;

FIG. 5 is an illustration of a semi-levered landing gear assembly inaccordance with an advantageous embodiment;

FIG. 6 is an illustration of a semi-levered landing gear of an airplaneduring initial touchdown in accordance with an advantageous embodiment;

FIG. 7 is an illustration of a semi-levered landing gear of an airplaneduring touchdown in accordance with an advantageous embodiment;

FIG. 8 is an illustration of a semi-levered landing gear of an airplaneduring touchdown in accordance with an advantageous embodiment;

FIG. 9 is an illustration of a semi-levered landing gear of an airplanein a static state on the ground in accordance with an advantageousembodiment;

FIG. 10 is an illustration of a semi-levered landing gear in a steadystate orientation in accordance with an advantageous embodiment;

FIG. 11 is an illustration of a sensor connected to a semi-leveredlanding gear in accordance with an advantageous embodiment;

FIG. 12 is an illustration of a diagram of a semi-levered landing gearwith positioning springs in a steady state in accordance with anadvantageous embodiment;

FIG. 13 is an illustration of a semi-levered linkage assembly in alocked state in accordance with an advantageous embodiment;

FIG. 14 is an illustration of a sensor connected to a semi-leveredlinkage assembly in a locked state in accordance with an advantageousembodiment;

FIG. 15 is an illustration of a diagram of a semi-levered linkageassembly with a tension load applied during initial ground contact inaccordance with an advantageous embodiment;

FIG. 16 is an illustration of a diagram of a semi-levered linkageassembly with a compression load in accordance with an advantageousembodiment;

FIG. 17 is an illustration of a graph of a load applied to asemi-levered landing gear linkage assembly versus rotation at an apexjoint in accordance with an advantageous embodiment; and

FIG. 18 is an illustration of a flowchart of a process for detecting aninitial touchdown of a semi-levered landing gear in accordance with anadvantageous embodiment.

DETAILED DESCRIPTION

Referring more particularly to the drawings, advantageous embodiments ofthe disclosure may be described in the context of aircraft manufacturingand service method 100 as shown in FIG. 1 and aircraft 200 as shown inFIG. 2. Turning first to FIG. 1, an illustration of an aircraftmanufacturing and service method is depicted in accordance with anadvantageous embodiment. During pre-production, aircraft manufacturingand service method 100 may include specification and design 102 ofaircraft 200 in FIG. 2 and material procurement 104.

During production, component and subassembly manufacturing 106 andsystem integration 108 of aircraft 200 in FIG. 2 takes place.Thereafter, aircraft 200 in FIG. 2 may go through certification anddelivery 110 in order to be placed in service 112. While in service 112by a customer, aircraft 200 in FIG. 2 is scheduled for routinemaintenance and service 114, which may include modification,reconfiguration, refurbishment, and other maintenance or services.

Each of the processes of aircraft manufacturing and service method 100may be performed or carried out by a system integrator, a third party,and/or an operator. In these examples, the operator may be a customer.For the purposes of this description, a system integrator may include,without limitation, any number of aircraft manufacturers andmajor-system subcontractors; a third party may include, withoutlimitation, any number of vendors, subcontractors, and suppliers; and anoperator may be an airline, a leasing company, a military entity, aservice organization, and so on.

With reference now to FIG. 2, an illustration of an aircraft is depictedin which an advantageous embodiment may be implemented. In this example,aircraft 200 is produced by aircraft manufacturing and service method100 in FIG. 1 and may include airframe 202 with a plurality of systems204 and interior 206. Examples of systems 204 include one or more ofpropulsion system 208, electrical system 210, hydraulic system 212,environmental system 214, and air-ground detection system 216.Air-ground detection system 216 is described further herein, such aswith respect to FIGS. 3-18. Any number of other systems may be included.Although an aerospace example is shown, different advantageousembodiments may be applied to other industries, such as the automotiveindustry. Apparatuses and methods embodied herein may be employed duringat least one of the stages of aircraft manufacturing and service method100 in FIG. 1.

In one illustrative example, components or subassemblies produced incomponent and subassembly manufacturing 106 in FIG. 1 may be fabricatedor manufactured in a manner similar to components or subassembliesproduced while aircraft 200 is in service 112 in FIG. 1. As yet anotherexample, a number of apparatus embodiments, method embodiments, or acombination thereof may be utilized during production stages, such ascomponent and subassembly manufacturing 106 and system integration 108in FIG. 1. A number, when referring to items, means one or more items.For example, a number of apparatus embodiments is one or more apparatusembodiments.

A number of apparatus embodiments, method embodiments, or a combinationthereof may be utilized while aircraft 200 is in service 112 and/orduring maintenance and service 114 in FIG. 1. The use of a number of thedifferent advantageous embodiments may substantially expedite theassembly of and/or reduce the cost of aircraft 200. For example,different advantageous embodiments may be used to add, upgrade, or useair-ground detection system 216 in aircraft 200. For example, air-grounddetection system 216, in accordance with an advantageous embodiment, maybe manufactured during component and subassembly manufacturing 106 addedto aircraft 200 during system integration 108 and used during in service112. As another illustrative example, air-ground detection system 216may be added to aircraft 200 during maintenance and service 114.

The different advantageous embodiments recognize and take into account anumber of different considerations. For example, different advantageousembodiments recognize and take into account that not all air-grounddetection systems are appropriate for all types of landing gear. Forexample, such a system may not be appropriate or optimal for use in anaircraft that uses a semi-levered landing gear.

The different advantageous embodiments recognize and take into accountthat another type of air-ground detection system for semi-leveredlanding gears may use strain gauges connected to axles or truck beams todetect early ground contact. A strain gauge measures strain on anobject. A strain gauge may be used to detect strain on a component, suchas an axle or a truck beam, caused by an increased load applied to thecomponent when the wheels touch the ground. The detected strainindicates that the vehicle has touched down. The different advantageousembodiments recognize and take into account that strain gauges, however,may have a limited life and may not be as reliable as desired.

The advantageous embodiments described herein recognize and take intoaccount one or more of the issues described above. Thus, the differentadvantageous embodiments provide a method and apparatus for anair-ground detection system. In an advantageous embodiment, asemi-levered landing gear fixedly positions the truck beam with respectto the shock absorber during takeoff and landing. During landing, thesemi-levered landing gear assembly is lowered with the forward axlehigher than the aft axle in a toes up position. Upon touchdown, wheelson the forward axle and the aft axle equally bear the weight of theaircraft.

In an advantageous embodiment, a semi-levered landing gear may constrainrotation of the truck beam such that truck beam rotation might not beusable as an early indicator of ground contact. Instead, a semi-leveredlanding gear air-ground detection system may use shock absorbercompression as an early indicator of ground contact. This systemattempts to detect rotation of the truck beam or compression of theshock absorber to indicate ground contact. However, this shock absorbercompression system may require more load on the shock absorber to rotatethe truck beam or compress the shock absorber than is used byconventional air-ground detection systems. As a result, this system maybe less sensitive.

Turning now to FIG. 3, an illustration of a block diagram of anair-ground detection system is depicted in which an advantageousembodiment may be implemented. Air-ground detection system 300illustrates one example of components that may be used in air-grounddetection system 216 in FIG. 2. In this particular example, air-grounddetection system 300 is configured to detect initial ground contact withthe ground 301 or any other surface by semi-levered landing gear 302.

Semi-levered landing gear 302, in this illustrative example, includestruck beam 304 mounted on pivot pin 306. Truck beam 304 may also bereferred to as a bogie beam. Truck beam 304 rotates or pivots aboutpivot pin 306 to toes up position 308.

In these examples, toes up position 308 is a position in which at leastone front wheel of semi-levered landing gear 302 is positioned higherthan at least one aft wheel connected to semi-levered landing gear 302.An illustration of toes up position 308 is shown in FIGS. 5-7.

In this illustrative example, toes up position 308 is an attitude inwhich truck beam 304 is positioned at a first angle 330. First angle 330may be any angle of truck beam 304 in which one or more wheels mountedon the front axle of semi-levered landing gear 302 are higher than thatof one or more wheels mounted on an aft axle of semi-levered landinggear 302.

In an advantageous embodiment, first angle 330 is an angle between arange of about forty (40) degrees and about eighty (80) degrees. Inanother advantageous embodiment, first angle 330 is about sixty (60)degrees. These angles may be less than or greater than theaforementioned values.

Positioning mechanism 332 is connected to locking mechanism 314. Lockingmechanism 314 is connected to truck beam 304. Positioning mechanism 332may secure truck beam 304 in toes up position 308 prior to initialground contact with the ground 301, such as, without limitation, duringtouchdown in a landing procedure.

Steady state 316 is an orientation of locking mechanism 314 in whichtension loads and/or compression loads applied to locking mechanism 314are insufficient to change steady state 316 to locked state 318. Theterm “steady state” may refer to the aircraft being fully in the air.

The term “tension load” refers to the force of pull supplied by strings,ropes, chains, or other members. The tension load may also be calledtension force. A compression load is a force or pressure that attemptsto compress, flatten, or squeeze a material. The term “compression load”refers to a pushing force. Tension load is the opposite of compressionload.

Steady state 316 may also be referred to as a free state. Anillustrative example of a landing gear in a steady state orientation isshown in FIG. 10 below.

Locked state 318 is an orientation of locking mechanism 314 when tensionloads applied to locking mechanism 314 are sufficient to move one ormore members of locking mechanism 314.

In another advantageous embodiment, locking mechanism 314 changes fromsteady state 316 to locked state 318 when the tension load onsemi-levered landing gear 302 is sufficient to rotate truck beam 304 apre-determined degree of rotation. The pre-determined degree of rotationmay be any degree of rotation that places truck beam 304 at second angle320. Second angle 320 is an angle that is greater than first angle 330.In other words, second angle 320 is an angle that positions the forwardaxle at a lower toes up position than first angle 330.

In an advantageous embodiment, second angle 320 is about one tenth (0.1)of a degree or greater than first angle 330. For example, if first angle330 is sixty (60) degrees, second angle 320 may be about 60.1 degrees.These angles are illustrative examples only, and may be varied. Lockingmechanism 314, in this advantageous embodiment, remains in steady state316 prior to semi-levered landing gear 302 making initial ground contactwith the ground 301.

As used herein, “initial ground contact” refers to some member ofsemi-levered landing gear 302 touching down on the ground 301. Forexample, without limitation, initial ground contact may refer to one ormore wheels on semi-levered landing gear 302 touching the ground 301during landing. In one advantageous embodiment, initial ground contactoccurs when an aft tire of the semi-levered landing gear contacts theground 301 or another surface during landing of an aircraft.

Prior to initial ground contact, semi-levered landing gear 302 does nothave any member or component in contact with the ground 301, such as,for example, without limitation, throughout retraction or extension ofsemi-levered landing gear 302. Upon touchdown, truck beam 304 pivotsabout pivot pin 306, imparting a tension load in locking mechanism 314.The load in semi-levered landing gear 302 is changed, causing lockingmechanism 314 to move from steady state 316 to locked state 318.

The changing orientation of locking mechanism 314 from steady state 316to locked state 318 may be detected using sensor 322. Sensor 322 may beimplemented as, for example, without limitation, any type of standardproximity sensor, contact switch, pressure sensor, rotary variabledifferential transformer (RVDT), linear variable differentialtransformer (LVDT), or any other displacement sensing technologies.

In this illustrative example, sensor 322 is connected to lockingmechanism 314. Sensor 322 detects a change in orientation of lockingmechanism 314 from steady state 316 to locked state 318. This changeindicates that semi-levered landing gear 302 has made initial groundcontact with the ground 301.

Thus, in this illustrative example, air-ground detection system 300 isconfigured such that semi-levered landing gear 302 may remain locked ina semi-lever mode on landing. Locking mechanism 314 may be in an almostlocked position until touchdown occurs. Upon touchdown, the weight ofthe airplane or other vehicle associated with semi-levered landing gear302 pulls locking mechanism 314 completely into locked state 318.

In other words, the weight of the vehicle settling on semi-leveredlanding gear 302 may result in an increased tension load on lockingmechanism 314 which changes locking mechanism 314 from steady state 316to locked state 318. Sensor 322 senses this motion as locking mechanism314 changes from steady state 316 to locked state 318.

The illustration of semi-levered landing gear 302 in FIG. 3 is not meantto imply physical or architectural limitations to the manner in whichdifferent advantageous embodiments may be implemented. Other componentsin addition to and/or in place of the ones illustrated may be used. Somecomponents may be unnecessary in some advantageous embodiments. Also,the blocks are presented to illustrate some functional components. Oneor more of these blocks may be combined and/or divided into differentblocks when implemented in different advantageous embodiments. Forexample, the advantageous embodiments could be in an aircraft such as anairplane or other aerospace vehicle.

Turning now to FIG. 4, an illustration of a block diagram of a vehicleis depicted in which an advantageous embodiment may be implemented.Vehicle 400 may be aircraft 200 in FIG. 2 or any other vehicle in whicha landing gear or an air-ground detection system might be used, such as,without limitation, aerospace vehicles.

Vehicle 400 may include fuselage 402, which is connected to wing 404.Semi-levered landing gear assembly 406 may be connected to at least oneof fuselage 402, wing 404, and actuator 408. Semi-levered landing gear406 may be, for example, without limitation, a landing gear in vehicle400, such as semi-levered landing gear 302 in FIG. 3.

Actuator 408 may be any mechanism for changing the orientation of atruck beam. Actuator 408 may be, for example, without limitation, ahydraulic actuator, an electric motor, or any other suitable type ofactuator.

In an advantageous embodiment, semi-levered landing gear assembly 406includes truck beam 410 connected to shock absorber 411. Shock absorber411 may also be referred to as a shock strut or an oleo.

Truck beam 410 is a tiltable truck beam. “Tiltable” refers to theability of truck beam 410 to rotate about pivot pin 412 and to tilt upor tilt down. Truck beam 410 may be truck beam 304 in FIG. 3.

Truck beam 410 is mounted on pivot pin 412. Pivot pin 412 provides apivot point for rotation of truck beam 410. Truck beam 410 rotates aboutpivot pin 412. In these illustrative examples, pivot pin 412 enablestruck beam 410 to rotate from a toes up position to a toes downposition. Pivot pin 412 may be implemented as a pivot point, such as,for example, without limitation, pivot pin 306 in FIG. 3.

In an advantageous embodiment, truck beam 410 may rotate from a level oran approximately horizontal position to the toes up position. In anotheradvantageous embodiment, truck beam 410 may rotate about pivot pin 412from the toes down position to the toes up position. The toes upposition may be a position such as toes up position 308 in FIG. 3.

As described above, the toes up position refers to a position in whichone or more wheels mounted on the front axle of semi-levered landinggear assembly 406 are positioned higher than one or more wheels mountedon the aft axle of semi-levered landing gear assembly 406.

In this illustrative example, truck beam 410 supports a number of frontwheels 414 on the front axle and a number of aft wheels 416 on the aftaxle. As used herein, a number of items refers to one or more items.

Additionally, the advantageous embodiments are not limited toimplementation with landing gear that have wheels mounted on only twoaxles. The advantageous embodiments may be implemented with landing gearthat have wheels mounted on two axles, three axles, or any other numberof axles supporting one or more wheels. In other words, there may be aplurality of additional axles between the forward axle supporting theforward wheels and the aft axle supporting the aft wheels.

Number of front wheels 414 may include one or more wheels. Number of aftwheels 416 may, likewise, include one or more wheels. Number ofpositioning springs 418 may include one or more positioning springs,such as, for example, without limitation, tension spring 440 andcompression spring 422.

Number of positioning springs 418 may be connected to one or more linksin number of links 425 within semi-levered linkage assembly 424. In anadvantageous embodiment, semi-levered linkage assembly 424 is acomponent of a locking mechanism, such as, for example, withoutlimitation, locking mechanism 314 in FIG. 3.

In this advantageous embodiment, semi-levered linkage assembly 424includes, without limitation, number of links 425 jointed together. Alink in number of links 425 may be a single member of the semi-leveredlinkage assembly. A link may also be referred to as a linkage arm.

Number of positioning springs 418 may be adapted to exert forcesrequired to hold the steady state position of semi-levered linkageassembly 424 to resist the aerodynamic forces applied to semi-leveredlanding gear assembly 406, such as, without limitation, air loads.Number of positioning springs 418 holds semi-levered linkage assembly424 in the steady state position prior to initial ground contact.

In this example, number of positioning springs 418 may include one ormore positioning springs. Number of positioning springs 418 may include,for example, without limitation, tension spring 440 and compressionspring 422. Tension spring 440 and compression spring 422 may be adaptedto exert force in opposition to one another to secure an angle of truckbeam 410 in a toes up position and secure semi-levered linkage assembly424 in a steady state, such as steady state 316 in FIG. 3, or asdescribed elsewhere herein.

In these illustrative examples, touchdown occurs when at least one wheelin number of aft wheels 416 comes in contact with the ground. When touchdown occurs, tension load on semi-levered linkage assembly 424increases. This increase in load on semi-levered linkage assembly 424may be sufficient to overcome the load on one or more springs in numberof positioning springs 418. This increase in load may move at least onelink in number of links 425 from the steady state into the locked state.

In one advantageous embodiment, compression spring 422 may be installedwith a pre-load greater than the load capability of tension spring 440.The pre-load may be achieved by installing compression spring 422 withincartridge 441 or other retention device that limits the maximum lengthof compression spring 422. In this manner, the steady state position ofsemi-levered linkage assembly 424 may be specifically determined.

Compression spring 422 may be restrained in a pre-loaded position withincartridge 441 or some other retention device such that compressionspring 422 cannot push against a second link within number of links 425past the steady state position. This may be done to achieve the steadystate condition.

In one advantageous embodiment, compression spring 422 within number ofpositioning springs 418 of a positioning mechanism may be connected,directly or indirectly, to a link within number of links 425 of thelocking mechanism. Compression spring 422 may be restrained in apre-loaded position. The pre-loaded position is an attitude in whichcompression spring 422 is prevented from applying force to a second linkwithin number of links 425 of the locking mechanism when the lockingmechanism is compressed beyond the steady state position. As usedherein, the term “compressed beyond the steady state” means the lockingmechanism is compressed to an extent that is beyond a position of thelocking mechanism that occurs when the vehicle or semi-levered landinggear assembly 406 is in the steady state.

In one advantageous embodiment, if compression spring 422 is not limitedto the steady state position, semi-levered linkage assembly 424 mayclose to a new steady state position. This position may not be as stableas desired, because forces exerted by tension spring 440 and compressionspring 422 may cancel each other out. A small amount of tension orcompression may cause the mechanism to move.

The advantageous embodiments recognize that it may be undesirable tohave semi-levered linkage assembly 424 move under tension or compressionvalues lower than a pre-determined load value. In one advantageousembodiment, the pre-determined load value may be a value within a rangeof about 100 to 500 pounds. In another advantageous embodiment, thepre-determined load value is about 400 pounds.

Number of positioning springs 418 also serves to hold the linkageassembly in the steady state position so that the linkage assembly holdsthe truck beam 410 in the correct orientation when semi-levered landinggear assembly 406 is retracted. The spring forces are calculated to holdthe linkage in the steady state position to resist the force of gravityand inertia acting on semi-levered linkage assembly 424 and truck beam410 during maneuvering of vehicle 400.

In an advantageous embodiment, semi-levered linkage assembly 424 may beconnected to number of positioning springs 418 in a steady stateorientation prior to number of aft wheels 416 making contact with theground, such as, for example, without limitation, during a landingprocedure for vehicle 400. At touchdown, the tension load onsemi-levered linkage assembly 424 increases. Due to this increase intension load, number of links 425 within semi-levered linkage assembly424 changes orientation from the steady state to a locked state uponinitial ground contact of number of aft wheels 416 with the ground.

In one advantageous embodiment, for example, without limitation, achange in the tension load on semi-levered linkage assembly 424 that isgreater than a pre-determined load value overcomes the force exerted bycompression spring 422 to lock semi-levered linkage assembly 424.

However, the advantageous embodiments are not limited to locking underloads of about 400 pounds or more. The advantageous embodiments may beimplemented to lock semi-levered linkage assembly 424 under a variety oftension loads. In this manner, one or more links within number of links425 changes orientation from the steady state to the locked state whensemi-levered landing gear 406 makes initial ground contact with theground.

Proximity sensor 426 may be connected to semi-levered landing gearassembly 406. Proximity sensor 426 detects a change in orientation ofnumber of links 425 within semi-levered linkage assembly 424 from thesteady state to the locked state indicating occurrence of the initialground contact.

In one advantageous embodiment, when proximity sensor 426 detects themovement of number of links 425 as semi-levered linkage assembly 424changes state from the steady state to the locked state, proximitysensor 426 generates signal 428 indicating that the initial groundcontact has occurred. Signal 428 may include sensor data 429 captured orgenerated by proximity sensor 426. Proximity sensor 426 sends signal 428and/or sensor data 429 indicating the initial ground contact to therelevant vehicle systems. The relevant vehicle systems may use theindication of initial ground contact with the ground to performfunctions, such as, for example, without limitation, deploying spoilersand applying brakes.

Vehicle 400 may optionally include a flight computer, such as dataprocessing system 430. Data processing system 430 may be implemented asany type of computing device on board vehicle 400. Data processingsystem 430 may be implemented as one or more data processing systemsincluding one or more processors and one or more tangible forms ofcomputer memory, such as, for example, but not limited to, random accessmemory, hard disk drives, and other suitable tangible forms of computermemory. In yet other illustrative examples, data processing system 430not be a general purpose computer with software. Instead, dataprocessing system 430 may be a device with a number of circuitsconfigured to perform desired functions and/or processes. These numberof circuits may include, for example, at least one of an integratedcircuit, an application specific integrated circuit, a programmablearray logic, a programmable logic array, a general logic array, a fieldprogrammable gate array, a programmable logic device, a complexprogrammable logic device, a programmable logic controller, a macrocellarray, and other suitable types of circuits.

Data processing system 430 may execute logic 433 to identify a sequenceof indicated locking mechanism un-commanded movements associated withthe change in state of semi-levered linkage assembly 406 from the steadystate orientation to the locked state orientation. Logic 433 may comparethe sequence of locking mechanism un-commanded movements to a number ofsensed flight phase indications to positively identify initial groundcontact. The term “sensed flight indicators” refers to flight indicatorssuch as, for example, without limitation, throttle position and/or shockabsorber compression.

Sensed flight indicators are not limited to only throttle positionand/or shock absorber compression. The advantageous embodiments do notrequire use of throttle position and/or shock absorber compression. Theadvantageous embodiments may use sensor data 429 from any other sensordevices associated with vehicle 400. Optionally, data from dataprocessing system 430 may include a flight computer, which may be usedas the sensor data 429.

The illustration of vehicle 400 in FIG. 4 is not meant to imply physicalor architectural limitations to the manner in which differentadvantageous embodiments may be implemented. Other components inaddition to and/or in place of the ones illustrated may be used. Somecomponents may be unnecessary in some advantageous embodiments. Also,the blocks are presented to illustrate some functional components. Oneor more of these blocks may be combined and/or divided into differentblocks when implemented in different advantageous embodiments. Forexample, semi-levered linkage assembly 424 might be considered part ofthe positioning mechanism 332. Shock absorber 411 need not be consideredpart of semi-levered landing gear assembly 406.

FIGS. 5-11 are illustrations of a semi-levered landing gear in usedepicted in accordance with an advantageous embodiment. Therefore, FIGS.5-11 share the same reference numerals and may correspond to the samecomponents and have similar structure and functions.

The advantageous embodiments shown in FIGS. 5-11 illustrate oneimplementation for semi-levered landing gear assembly 406 in FIG. 4 andair-ground detection system 216 in FIG. 2. Not all components describedwith respect to FIG. 4 are necessarily shown with respect to FIGS. 5-11;however, all such components may be present in some advantageousembodiments. Moreover, the advantageous embodiments described herein maynot be limited to the components in precisely the same configuration asshown in FIGS. 5-11.

With reference now to FIG. 5, an illustration of a semi-levered landinggear is depicted in accordance with an advantageous embodiment.Semi-levered landing gear 500 is an example of one implementation forsemi-levered landing gear assembly 406 in FIG. 4.

As depicted in this illustrative example, semi-levered landing gear 500is connected to shock strut 502 extending downwardly from the fuselageof an aircraft or other vehicle. Shock strut 502 generally includesouter cylinder 503 and inner cylinder 510. Shock strut 502 may also bereferred to as a shock absorber, or may be part of a shock absorber,such as shock absorber 411 of FIG. 4. Semi-levered landing gear 500 isalso connected to truck beam 506 pivotally connected to inner cylinder510 by pivot pin 508. Truck beam 506 includes front end 505 and opposedaft end 507. Front end 505 of truck beam 506 includes front axle 514and, similarly, aft end 507 includes aft axle 512. As shown in FIG. 5,one or more of wheels 511 may be mounted upon front axle 514 and aftaxle 512 for take-off, taxi, and landing and also to support theaircraft during ground operations.

In FIG. 5, semi-levered landing gear 500 is depicted in a steady state.As defined above, a steady state is an orientation of the lockingmechanism in which tension loads and/or compression loads applied to thelocking mechanism are insufficient to change the steady state to alocked state. Steady state position may be a state such as, withoutlimitation, steady state 316 in FIG. 3. A steady state position may beheld while a vehicle is descending on approach to a landing area, butnot yet touching the ground.

Semi-levered landing gear 500 may be a semi-levered landing gearassembly associated with a vehicle, such as, for example, withoutlimitation, an airplane or other aircraft. Semi-levered landing gear 500may be a landing gear, such as semi-levered landing gear 302 in FIG. 3or semi-levered landing gear assembly 406 in FIG. 4.

Semi-levered landing gear 500 is shown extended outside a wheel well ofan aircraft during flight in a steady state while the aircraft is in theair upon approach. Pivot pin 508 connects truck beam 506 to innercylinder 510. Pivot pin 508 may be a pivot point for truck beam 506.Pivot pin 508 may be pivot pin 306 in FIG. 3 and/or pivot pin 412 inFIG. 4.

Positioning system 515 positions truck beam 506 in a fixed, toes-upattitude. As described above, the toes-up attitude refers to a positionin which truck beam 506 is tilted at an angle such that front axle 514is higher than aft axle 512, such as, for example, without limitation,steady state 316 in FIG. 3.

Still referring to FIG. 5, semi-levered landing gear 500 also includessemi-levered linkage assembly 504. Semi-levered linkage assembly 504 mayalso comprise a number of links, such as, for example, withoutlimitation, number of links 425 in FIG. 4, for angularly orienting truckbeam 506. Semi-levered linkage assembly 504 has a large moment arm toresist rotation of truck beam 506 in the steady state until apre-determined load value is reached. As described above, a steady stateis an orientation of the locking mechanism in which tension loads and/orcompression loads applied to the locking mechanism are insufficient tochange the steady state to a locked state.

The steady state tension and compression capability of semi-leveredlinkage assembly 504 in this advantageous embodiment may have apre-determined load value. In one illustrative example, thispre-determined load value may be a value in a range between about 100 toabout 500 pounds, but may be less than or greater than these values.

The pre-determined load value is any pre-determined load amount thattriggers the change in orientation of semi-levered linkage assembly 504.In this advantageous embodiment, semi-levered linkage assembly 504 opensto a locked position for a pre-determined tension load value. Thepre-determined tension load value may be any value in a range betweenabout 100 and 700 pounds. In one advantageous embodiment, thepre-determined tension load value is greater than or equal to about 200pounds. The pre-determined tension load may be greater than or less thanthese values.

Likewise, semi-levered linkage assembly 504 folds closed under acompression load that reaches a pre-determined compression load value.In this example, semi-levered linkage assembly 504 folds closed under acompression load that is greater than about 200 pounds, though thisvalue may vary. However, the advantageous embodiments are not limited toopening in a locked position at a pre-determined load value of about 200pounds. The pre-determined load value may be about 100 pounds, about 270pounds, about 500 pounds, or any other value of the pre-determined loadvalue.

Turning now to FIG. 6, an illustration of a semi-levered landing gear ofan airplane during initial touchdown is depicted in accordance with anadvantageous embodiment. Initial touchdown position 600 for semi-leveredlanding gear 500 occurs when aft wheels 602 make contact with ground 604for the first time during landing. Initial touchdown position 600 may bea position for a semi-levered landing gear, such as semi-levered landinggear 500 in FIG. 5.

Semi-levered landing gear 500 is in a fixed, toes-up attitude in whichtruck beam 506 is tilted at an angle such that front axle 514 is higherthan aft axle 512. As described above, the toes up position is aconfiguration in which the forward wheels on the main landing gear areat a higher position than that of the rear wheels on the main landinggear. During initial touchdown, truck beam 506 undergoes acounterclockwise rotation 606 about pivot pin 508, thereby creating atension load in semi-levered linkage assembly 504. The tension loadvector is shown by arrow 608.

Sensor 610 may be connected to semi-levered linkage assembly 504. Sensor610 may be implemented as any type of proximity sensor, such as, withoutlimitation, sensor 322 in FIG. 3 or proximity sensor 426 in FIG. 4.Sensor 610 may sense that semi-levered linkage assembly 504 has beenloaded in tension, indicating that the aft wheels 602 have touched down.The sensor is described further with respect to FIG. 11.

With reference now to FIG. 7, an illustration of a semi-levered landinggear of an airplane during touchdown is depicted in accordance with anadvantageous embodiment. Continued touchdown position 700 may be aposition for a semi-levered landing gear, such as semi-levered landinggear 500 of FIG. 5.

Continued touchdown position 700 is a position of semi-levered landinggear 500 as inner cylinder 510 compresses, as shown by arrow 704, underthe weight of the airplane as the aft wheels 602 make continued contactwith ground 604.

Semi-levered landing gear 500 may be in a fixed, toes-up attitude, inwhich truck beam 506 is tilted at an angle such that front axle 514 ishigher than aft axle 512. Pivot pin 508 connects truck beam 506 to innercylinder 510. Truck beam 506 continues to undergo the counterclockwiserotation 606 about pivot pin 508 as the tension load in semi-leveredlinkage assembly 504 increases under the weight of the airplane as theairplane settles onto semi-levered landing gear 500. The tension loadvectors are shown by arrow 608 and arrow 702. In other words, thetension load, as shown by arrows 608 and 702, increases because anincreasing amount of the weight of the airplane is settling onsemi-levered landing gear 500.

Turning now to FIG. 8, an illustration of a semi-levered landing gear ofan airplane at touchdown is depicted in accordance with an advantageousembodiment. Front wheel touchdown position 800 may be a position for asemi-levered landing gear, such as semi-levered landing gear 500 in FIG.5.

Front wheel touchdown position 800 is a position of semi-levered landinggear 500 as inner cylinder 510 continues to compress under the weight ofthe airplane, as shown by arrow 802. Truck beam 506 continues to undergocounterclockwise rotation 606 until front wheels 804 contacts ground604. In this illustrative example, truck beam 506 is approximatelyparallel with ground 604 such that front axle 514 is about level withaft axle 512.

The tension load in semi-levered linkage assembly 504 is relieved as theweight of the aircraft is distributed across front wheels 804 and aftwheels 602. Thus, as the airplane continues to settle to the ground,inner cylinder 510 compresses until front wheels 804 touch ground 604.

Referring now to FIG. 9, an illustration of a semi-levered landing gearof an airplane in a static state on the ground is depicted in accordancewith an advantageous embodiment. Ground position 900 may be a positionfor a semi-levered landing gear, such as semi-levered landing gear 500in FIG. 5.

An airplane fully in ground position 900 is in a position in which thefull weight of the airplane is resting on the landing gears. This statemay be referred to as a landed static state. In an advantageousembodiment, the airplane in the landed static state may be rolling downthe runway, taxiing to the terminal, or stationary.

In this illustrative example, the airplane's front axle 514 and aft axle512 are approximately parallel with ground 604. Aft wheels 602 connectedwith aft axle 512 are in contact with ground 604.

Inner cylinder 510 is fully compressed under the weight of the airplane,as shown by arrow 902. Semi-levered linkage assembly 504 is compressedunder the load from front axle 514. The compression load on semi-leveredlinkage assembly 504 is shown by arrows 904.

The compression load in semi-levered linkage assembly 504 is greaterthan the free state load. In this example, continued compression ofinner cylinder 510 unlocks semi-levered linkage assembly 504 whichdisengages semi-levered landing gear 500. Further detail regardingsemi-levered linkage assembly 504 and related springs and sensors isdescribed with respect to FIG. 11.

With reference now to FIG. 10, an illustration of a semi-levered landinggear in a steady state orientation is depicted in accordance with anadvantageous embodiment. Semi-levered landing gear 1000 is a landinggear, such as semi-levered landing gear 302 in FIG. 3 and semi-leveredlanding gear assembly 406 in FIG. 4. Semi-levered landing gear 1000,which may also be semi-levered landing gear 500 of FIG. 5, is in asteady state in the air, as shown in FIGS. 3, 5, and 10. As definedabove, a steady state is an orientation of the locking mechanism inwhich tension loads and/or compression loads applied to the lockingmechanism are insufficient to change the steady state to a locked state.

Semi-levered linkage assembly 1002 includes a locking mechanism having anumber of links, such as, for example, without limitation, lockingmechanism 314 in FIG. 3 and semi-levered linkage assembly 424 in FIG. 4.

In this illustrative example, semi-levered linkage assembly 1002 keepstruck beam 1004 positioned at about a sixty (60) degree angle 1006 toesup until such time as the aft tires touchdown on the ground. However,the advantageous embodiments are not limited to implementation with asixty degree angle.

The advantageous embodiments may be implemented with semi-leveredlanding gear 1000 having truck beam 1004 positioned at any angle in atoes up position until such time as the aft tires touchdown on theground. For example, truck beam 1004 may be at about a 61 degree angle,about a 59 degree angle, about a 55 degree angle, about a 45 degreeangle, or any other suitable angle associated with a toes up position oftruck beam 1004. These angles may vary.

Turning now to FIG. 11, an illustration of a sensor connected to asemi-levered landing gear is depicted in accordance with an advantageousembodiment. Sensor 1100 is a sensor for detecting a change in state of asemi-levered linkage assembly, such as, without limitation, sensor 322in FIG. 3 or proximity sensor 426 in FIG. 4.

Sensor 1100, in this illustrative example, is a proximity sensor fordetecting a change in distance or gap 1102 between sensor 1100 andtarget 1104. However, the advantageous embodiments are not limited to aproximity sensor. The advantageous embodiments may be implemented usingany suitable type of sensor for detecting a displacement in a linkageassembly.

While a landing gear is in the air, the linkage assembly is in a steadystate, as shown in FIG. 10. While in the steady state, gap 1102 may be adistance between target 1104 and sensor 1100. In this example, gap 1102is a target far gap indicating that target 1104 is far from sensor 1100.A target far gap may be any distance between target 1104 and sensor 1100indicating a steady state orientation. In this advantageous embodiment,the target far gap is a distance greater than about 0.07 inches, thoughthis distance may vary by up to an inch or more.

With reference now to FIG. 12, an illustration of a diagram of asemi-levered landing gear with positioning springs in a steady state isdepicted in accordance with an advantageous embodiment. Semi-leveredlinkage assembly 1200 may be a locking mechanism such as, withoutlimitation, locking mechanism 314 in FIG. 3 and semi-levered linkageassembly 424 in FIG. 4.

Semi-levered linkage assembly 1200 may include first link 1202 andsecond link 1204. In one advantageous embodiment, but withoutlimitation, first link 1202 may be an upper link in semi-levered linkageassembly 1200 and second link 1204 may be a lower link of semi-leveredlinkage assembly 1200. Moreover, the advantageous embodiments are notlimited to a semi-levered linkage assembly having first link 1202 andsecond link 1204. Other advantageous embodiments may include asemi-levered linkage assembly having other additional links not shown inFIG. 12. Additionally, a tension load may be applied to semi-leveredlinkage assembly 1200 that is less than a pre-determined tension loadvalue.

Semi-levered linkage assembly 1200 may be secured in a steady state bytwo positioning springs, such as, for example, without limitation,tension spring 1206 and compression spring 1208. Tension spring 1206, inthis illustrative example, is connected to both first link 1202 andsecond link 1204. Compression spring 1208, in this illustrative example,is only connected to first link 1202. Tension spring 1206 andcompression spring 1208 may be implemented using coil springs,Belleville springs, pneumatic springs, lever springs, or any othersuitable type of tension and compression springs.

Tension spring 1206 and compression spring 1208 work against each otherto position semi-levered linkage assembly 1200 in the steady stateorientation. Tension spring 1206 and compression spring 1208 arepositioning springs sized to prevent air loads, retraction loads, andmaneuver loads from disturbing the position of the truck beam.

In one advantageous embodiment, tension spring 1206 may hold first link1202 and second link 1204 in the steady state under compression loadsless than a pre-determined compression load value. In this advantageousembodiment, semi-levered linkage assembly 1200 includes at least onesensor for detecting when semi-levered linkage assembly 1200 has beendisplaced from the steady state orientation. The one or more sensors mayinclude sensors 1210, 1212, and 1214.

A sensor may be connected to semi-levered linkage assembly 1200 at avariety of positions to sense that semi-levered linkage assembly 1200has been loaded in tension, indicating that the aft tires of a landinggear have touched down. For example, sensor 1210 is mounted in-line withtension spring 1206. Sensor 1212 is mounted to first link 1202 proximateto compression spring 1208 and stop 1216. As used herein, a “stop” issome object that impedes an ability of another object to move withrespect to the stop. Sensor 1214 is mounted to a second location onsecond link 1204.

However, the advantageous embodiments are not limited to attaching asensor to only the three locations shown in FIG. 12. A sensor may beplaced on semi-levered linkage assembly 1200 at any other location suchthat the sensor may detect a displacement of one or more linkages insemi-levered linkage assembly 1200 from the steady state.

The sensors 1210, 1212, and 1214 in this illustrative example may beproximity sensors having a gap between the sensor and the targetassociated with that sensor, such as gap 1218, gap 1220, and gap 1222.In this illustrative example, the gap for each sensor indicates that thesensor is far from the sensor's associated target. For example, withoutlimitation, gap 1218 indicates sensor 1210 is far from the targetassociated with sensor 1210.

The advantageous embodiments are not limited to implementation usingproximity sensors. For example, sensor 1210 may be a linear variabledifferential transformer or string potentiometer located on a springaxis to measure a change in length of tension spring 1206. Likewise, asensor may be mounted at apex 1224 to measure a change in angle 1226between first link 1202 and second link 1204, such as a rotary variabledifferential transformer, a string potentiometer, a rotary encoder, orany other type of displacement sensing technology. The required springforce required to hold semi-levered linkage assembly 1200 in this steadystate position for a given load may be calculated using spring momentarm and linkage angle alpha 1228.

FIG. 12 is intended as an example, and not as an architecturallimitation, for the different advantageous embodiments. For example, theadvantageous embodiments in FIG. 12 illustrate three sensors. However,the advantageous embodiments do not require three sensors. An air-grounddetection system may only include one single sensor, as well as two ormore sensors.

For example, in FIG. 12, compression spring 1208 is shown connected tosecond link 1204. However, the advantageous embodiments are not limitedto attaching compression spring 1208 to second link 1204. Compressionspring 1208 may be connected to one or more other links of semi-leveredlinkage assembly 1200 to hold first link 1202 away from second link1204.

Compression spring 1208 need not be connected to second link 1204, butrather may be connected to some other link in semi-levered linkageassembly 1200. Compression spring 1208 may be connected to one link tofill the space between two links. In other words, compression spring1208 may be connected to a first link in order to hold the first linkaway from the second link.

Turning now to FIG. 13, an illustration of a semi-levered linkageassembly in a locked state is depicted in accordance with anadvantageous embodiment. Semi-levered landing gear 1300 is a landinggear such as semi-levered landing gear 302 in FIG. 3 and semi-leveredlanding gear assembly 406 in FIG. 4. Semi-levered landing gear 1300 isin a locked state at initial ground contact, such as initial touchdownposition 600 in FIG. 6. Semi-levered landing gear 1300 may besemi-levered landing gear 500 in FIG. 5.

Semi-levered linkage assembly 1302 may be a locking mechanism having anumber of links, such as, for example, without limitation, lockingmechanism 314 in FIG. 3 and semi-levered linkage assembly 424 in FIG. 4.Semi-levered landing gear 1300 may be a landing gear with a lockingmechanism such as, without limitation, locking mechanism 314 in FIG. 3and semi-levered linkage assembly 424 in FIG. 4.

When the landing gear connected to semi-levered linkage assembly 1300touches the ground during landing, truck beam 1304 pivots about a pivotpoint, such as pivot pin 508 in FIG. 5, and imparts a tension load insemi-levered linkage assembly 1302. If the tension load uponsemi-levered linkage assembly 1302 is greater than about 200 pounds,then the links in semi-levered linkage assembly 1302 overcome thecompression springs and lock semi-levered linkage assembly 1302 in thelocked state.

Semi-levered linkage assembly 1302, when locked, positions truck beam1304 at a pre-determined angle. In an advantageous embodiment, thispre-determined angle may be about 60.2 degrees 1306, though this valuemay be more or less. Thus, semi-levered linkage assembly 1302 may onlyundergo a pre-determined degree of rotation. In this example, thepre-determined degree of rotation may about two tenths (0.2) of a degreeof rotation. However, the advantageous embodiments are not limited totwo tenths of a degree of rotation. The advantageous embodiments may beimplemented using any pre-determined degree of rotation, such as, forexample, without limitation, three tenths (0.3) of a degree of rotation,five tenths (0.5) of a degree of rotation, or any other suitable greateror lesser pre-determined degree of rotation.

Other indication systems may use different degrees of rotation. Forexample, other indication systems may use five degrees of rotation ormore, which may require more load on the semi-levered landing gear toachieve that degree of rotation. The advantageous embodiments shown inFIG. 13 may require less load on the landing gear to achieve about twotenths (0.2) of a degree of rotation. Therefore, the advantageousembodiments shown in FIG. 13 may permit quicker indication of touchdown.

Referring now to FIG. 14, an illustration of a sensor connected to asemi-levered linkage assembly in a locked state is depicted inaccordance with an advantageous embodiment. Sensor 1400 may be a sensorfor detecting a change in the state of a semi-levered linkage assembly,such as, for example, without limitation, sensor 322 in FIG. 3 orproximity sensor 426 in FIG. 4.

Sensor 1400, in this illustrative example, may be a proximity sensor fordetecting a change in length of gap 1402 between sensor 1400 and target1404. However, the advantageous embodiments are not limited to aproximity sensor. The advantageous embodiments may be implemented usingany type of sensor for detecting a displacement in a semi-leveredlinkage assembly.

When the semi-levered landing gear touches the ground, the load on thesemi-levered landing gear increases, and thereby increases the load onthe semi-levered linkage assembly. The increase in tension load on thesemi-levered linkage assembly results in the links changing theirorientation from a steady state to a locked state.

Sensor 1400 may detect that the linkage changes from the steady state tothe locked state. This change in state results in a decrease in gap1402.

Gap 1402 indicates that target 1404 is near sensor 1400. Lack of any gapbetween target 1404 and sensor 1400 may indicate that the linkageassembly is in a locked state. In this case, at least one wheel of thesemi-levered landing gear has made initial ground contact with theground during landing.

FIG. 15 is an illustration of a diagram of a semi-levered linkageassembly with a tension load applied during initial ground contact inaccordance with an advantageous embodiment. Semi-levered linkageassembly 1500 is a locking mechanism such as, for example, withoutlimitation, locking mechanism 314 in FIG. 3 and semi-levered linkageassembly 424 in FIG. 4.

Semi-levered linkage assembly 1500 may include, for example, withoutlimitation, first link 1502 and second link 1504. First link 1502 andsecond link 1504 are links within semi-levered linkage assembly 1500.Semi-levered linkage assembly 1500 is not limited to including only twolinks. Semi-levered linkage assembly 1500 may include one or more otheradditional links not described or shown in FIG. 15.

Semi-levered linkage assembly 1500 may include two positioning springs,such as, for example, without limitation, tension spring 1506 andcompression spring 1508. Tension spring 1506 in this illustrativeexample is connected to first link 1502 and second link 1504.Compression spring 1508 may be connected to second link 1504. However,the advantageous embodiments are not limited to only including a singletension spring, such as tension spring 1506, with another singlecompression spring, such as compression spring 1508. In otheradvantageous embodiments, semi-levered linkage assembly 1500 may beconnected to one or more other springs not shown in FIG. 15.

Sensor 1510, sensor 1512, and sensor 1514 show only a near gap betweenthe sensors 1510, 1512, and 1514 and their respective targets 1516,1518, and 1520. For example, sensor 1510 has a near gap between it andtarget 1516. The term “near gap” is defined as a very small ornegligible gap distance, quantified as being between about onethousandth (0.001) of an inch and one tenth (0.1) of an inch, indicatingthat target 1516 is near sensor 1510. The near gap may be any gapdistance that is less than a far gap distance between target 1516 andsensor 1510. The term “far gap” is defined as a distance larger than anear gap.

These distances may vary. In an advantageous embodiment, a near gapdistance may be any distance that is three hundredths (0.03) of an inchless than the far gap. In another advantageous embodiment, the near gapdistance may be any distance within a range of one thousandth (0.001) ofan inch and nine hundredths (0.09) of an inch. In yet anotheradvantageous embodiment, the near gap may be about five thousandths(0.005) of an inch. In still another advantageous embodiment, a near gapdistance may be, for example, without limitation, any distance that isless than about four hundredths (0.04) of an inch.

In one advantageous embodiment, stop 1522 is connected to semi-leveredlinkage assembly 1500. Stop 1522 may hold semi-levered linkage assembly1500 in the locked state under tension loads exceeding thepre-determined tension load value.

Stop 1522 may be engaged to prevent additional rotation of semi-leveredlinkage assembly 1500 as tension load 1524 increases. In anotherillustrative example, stop 1522 may be engaged to stop rotation of atruck beam at a pre-determined degree of rotation in response to thechange from the steady state to the locked state.

With reference now to FIG. 16, an illustration of a diagram of asemi-levered linkage assembly with a compression load is depicted inaccordance with an advantageous embodiment. Semi-levered linkageassembly 1600 may include tension spring 1602 and compression spring1604. Compression load 1606 may be greater than the tension spring loadin tension spring 1602.

Compression spring 1604 is not engaged in this illustrative example.Further travel of compression spring 1604 in this example may beconstrained by cartridge 1608 in which stop 1610 is not engaged.

Thus, semi-levered linkage assembly 1600 may be folded closed undercompression load 1606. Compression load 1606, in this illustrativeexample, may be about 200 pounds or more. However, the advantageousembodiments are not limited to a compression load of about 200 pounds toovercome the tension spring load in tension spring 1602. Theadvantageous embodiments may be implemented to configure tension spring1602 such that a compression load that is equal to or less than about200 pounds may overcome the tension spring load.

Turning now to FIG. 17, an illustration of a graph of a load applied toa semi-levered landing gear linkage versus rotation at an apex joint isdepicted in accordance with an advantageous embodiment. The advantageousembodiments described herein with respect to FIG. 17 describe particularvalues. These particular values may vary in different advantageousembodiments. Graph 1700 shows rotation at an apex joint of asemi-levered linkage assembly under tension and compression loadsbetween zero to 1000 pounds.

Where the load applied to a semi-levered linkage assembly is betweenzero to 200 pounds, there is no rotation at the apex shown at segment1702. Rotation does not occur because number of positioning springs 418in FIG. 4 holds the semi-levered linkage assembly in the steady stateuntil the linkage assembly is forced open by tension loads greater than200 pounds, or forced closed by compression loads greater than 200pounds. Thus, in this illustrative example, the steady state range isplus or minus 200 pounds.

At segment 1704, the semi-levered linkage assembly opens under tensionloads higher than about 200 pounds. At two tenths (0.2) of a degree ofrotation, a stop connected to the semi-levered linkage assembly preventsthe semi-levered linkage assembly from undergoing additional rotation,even as the load increases. Segment 1706 shows increased load above 200pounds without increased rotation. In other words, once the load exceeds200 pounds, only 0.2 degrees of rotation occurs.

When the compression load reaches the pre-determined compression loadvalue of 200 pounds, as shown in segment 1708, the semi-levered linkageassembly folds closed. The angle of the curve at segment 1708 is afunction of the tension spring rate and spring effective moment arm.

Thus, a tension spring holds the semi-levered linkage assembly in asteady state under compression loads up to the pre-determinedcompression load value. When the compression load increases to the pointthat it exceeds the pre-determined compression load value, thesemi-levered linkage assembly folds closed.

Turning now to FIG. 18, an illustration of a flowchart of a process fordetecting an initial touchdown of a semi-levered landing gear isdepicted in accordance with an advantageous embodiment. The processdepicted in FIG. 18 may be implemented by an air-ground detection systemusing a proximity sensor or any other type of displacement sensingdevice, such as air-ground detection system 300 in FIG. 3. The processin FIG. 18 may also be implemented using semi-levered linkage assembly504 in FIG. 5, semi-levered landing gear 1000 in FIG. 10, andsemi-levered linkage assembly 1200 of FIG. 12. Any of these features maybe described as a “device” suitable for implementing the process of FIG.18.

The process begins by the device monitoring an orientation of a numberof links of a semi-levered linkage assembly (operation 1802). The numberof links may be number of links 425 in FIG. 4, and the semi-leveredlinkage assembly may be semi-levered linkage assembly 424 in FIG. 4.Then, the device detects whether a change occurs in the orientation ofthe semi-levered linkage assembly from a steady state (operation 1804).The steady state may be steady state 316 in FIG. 3.

If at operation 1804 there is no change detected in the orientation ofthe semi-levered linkage assembly from a steady state, the devicedetermines whether the steady state has changed to a locked state(operation 1808). A change from the steady state to the locked state maybe detected by a sensor, such as sensor 322 in FIG. 3. If, however, atoperation 1804 the device determines that a change is detected in theorientation of the semi-levered linkage assembly to a locked state, thedevice indicates an in-air position of the semi-levered landing gear(operation 1806). The process proceeds to operation 1808. Thesemi-levered landing gear may be semi-levered landing gear 302 in FIG.3.

At operation 1808, the device determines whether the semi-leveredlanding gear has changed from a steady state to a locked state. If atoperation 1808 the device determines that the steady state has notchanged to a locked state, the process returns to operation 1804. If,however, at operation 1808 the device determines that the steady statehas changed to a locked state, the device indicates an initial groundcontact position (operation 1810). The process terminates thereafter.

An indication of an in-air position in one advantageous embodiment maybe indicated by a lack of notification of any change or initial groundcontact. Referring again to FIG. 12, in an advantageous embodiment, anindication of an in-air position may also be indicated by tension spring1206 and compression spring 1208 working against each other to positionsemi-levered linkage assembly 1200 in the steady state orientation.

Thus, the different advantageous embodiments recognize and take intoaccount a number of considerations. For example, without limitation, thedifferent advantageous embodiments recognize and take into account thatsemi-levered landing gears might fix rotation of a truck beam, withrespect to the shock strut, to give certain performance advantagesduring takeoff and landing. However, the advantageous embodiments alsorecognize and take into account that semi-levered landing gears mightconstrain the rotation of the truck beam. When the truck beam is soconstrained, truck beam rotation might not be used as an early indicatorof ground contact by conventional air-ground detection systems. Theadvantageous embodiments described herein overcome this issue.

Therefore, an advantageous embodiment of the present disclosure providesa system for air-ground detection in semi-levered landing gear. A truckbeam of a semi-levered landing gear is mounted on a pivot pin. The truckbeam rotates from a toes up position to a toes down position. A toes upposition refers to a position in which the truck beam is angled upwardso that the front wheel or wheels on the semi-levered landing gear arepositioned higher than the aft wheel or wheels.

A positioning mechanism may be connected to a locking mechanism andadapted to secure an angle of the truck beam in the toes up position.The positioning mechanism may an actuator or motor or other means ofmoving the locking mechanism and the truck beam. In FIG. 5, positioningsystem 515 is shown as including three links and one actuator.

The locking mechanism may be secured in a steady state orientation by atension and compression spring or springs. The locking mechanism may besecured in a steady state condition for all conditions where the wheelsof the landing gear are in-air and not contacting the ground. Thepositioning mechanism connected to a semi-levered linkage assembly ofthe locking mechanism may move the semi-levered linkage assembly to thetoes up orientation prior to initial ground contact during a landingprocedure.

The locking mechanism may be implemented as, for example, withoutlimitation, a semi-levered linkage assembly. The semi-levered linkageassembly may optionally include a first link and a second link. Thelocking mechanism changes orientation from the steady state to a lockedstate upon initial ground contact.

A sensor connected to the locking mechanism may detect a change inorientation from the steady state to the locked state, indicatingoccurrence of the initial ground contact. The sensor may be implementedas, for example, without limitation, a proximity sensor or any othertype of displacement sensing mechanism.

These features, and optionally others described herein, allow theadvantageous embodiments to provide a reliable system for earlydetection of ground contact for a semi-levered landing gear thatenhances landing efficiency. The advantageous embodiments enable earlydetection of ground contact by landing gear wheels for quick spoilerdeployment and brake activation.

The advantageous embodiments also provide a quick and reliable touchdownindication that reduces landing roll length and brake wear. Theadvantageous embodiments recognize that sensing that the aft tires of anaircraft have touched down at an early stage of landing is desirable asa means for triggering other airplane systems, such as spoilerdeployment and braking systems.

The flowcharts and block diagrams in the different depicted advantageousembodiments illustrate the architecture, functionality, and operation ofsome possible implementations of apparatuses and methods in differentadvantageous embodiments. In this regard, each block in the flowchart orblock diagrams may represent a module, segment, function, and/or aportion of an operation or step. In some alternative implementations,the function or functions noted in the block may occur out of the ordernoted in the figures. For example, in some cases, two blocks shown insuccession may be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. Also, other blocks may be added in addition tothe illustrated blocks in a flowchart or block diagram.

As used herein, the phrase “at least one of”, when used with a list ofitems, means that different combinations of one or more of the listeditems may be used and only one of each item in the list may be needed.For example, “at least one of item A, item B, and item C” may include,for example, without limitation, item A or item A and item B. Thisexample may also include item A, item B, and item C or item B and itemC.

As used herein, a first component “connected to” a second componentmeans that the first component can be connected directly or indirectlyto the second component. In other words, additional components may bepresent between the first component and the second component. The firstcomponent is considered to be indirectly connected to the secondcomponent when one or more additional components are present between thetwo components. When the first component is directly connected to thesecond component, no additional components are present between the twocomponents.

The description of the different advantageous embodiments has beenpresented for the purposes of illustration and description, and is notintended to be exhaustive or limited to the advantageous embodiments inthe form disclosed. Many modifications and variations will be apparentto those of ordinary skill in the art. Further, different advantageousembodiments may provide different advantages as compared to otheradvantageous embodiments. The advantageous embodiment or advantageousembodiments selected are chosen and described in order to best explainthe principles of the advantageous embodiments, the practicalapplication, and to enable others of ordinary skill in the art tounderstand the disclosure for various advantageous embodiments withvarious modifications as are suited to the particular use contemplated.

1-9. (canceled)
 10. A method for air-ground detection in a semi-leveredlanding gear, the method comprising: monitoring an orientation of anumber of links of a semi-levered linkage assembly using a sensorconnected to the semi-levered linkage assembly, wherein the sensor isconfigured to detect a change from the steady state to the locked statewithout requiring a change in shock strut compression; and responsive todetecting a change in the orientation of the semi-levered linkageassembly from a steady state to a locked state, indicating an initialground contact position of the semi-levered landing gear.
 11. The methodof claim 10 further comprising: sending sensor data indicating thechange in the orientation of the semi-levered landing gear assembly to adata processing system of an aircraft to indicate the initial groundcontact position.
 12. The method of claim 10 further comprising:identifying, by a data processing system of an aircraft, a sequence ofindicated semi-levered linkage assembly un-commanded movementsassociated with the change in the orientation from the steady state tothe locked state; and comparing the sequence of indicated semi-leveredlinkage assembly un-commanded movements to a number of sensed flightphase indications to positively identify the initial ground contactposition.
 13. The method of claim 10 further comprising: holding thesemi-levered linkage assembly in the steady state under a tension loadless than a pre-determined tension load value; and responsive to thesemi-levered linkage assembly coming under the tension load exceedingthe pre-determined tension load value, moving the semi-levered linkageassembly into the locked state.
 14. The method of claim 10 furthercomprising: holding the semi-levered linkage assembly in the steadystate under a compression load less than a pre-determined compressionload value; and responsive to the semi-levered linkage assembly comingunder the compression load exceeding the pre-determined compression loadvalue, folding closed the semi-levered linkage assembly. 15-20.(canceled)
 21. The method of claim 10, wherein the semi-levered linkageassembly comprises a truck beam mounted on a pivot pin, and wherein themethod further comprises: rotating the truck beam between a toes upposition prior to landing a toes down position after an initial groundcontact.
 22. The method of claim 21, wherein the semi-levered linkageassembly further comprises a locking mechanism configured to secure anangle of the truck beam in the toes-up position, and wherein the methodfurther comprises: changing the locking mechanism from a steady state toa locked state in response to an initial ground contact.
 23. The methodof claim 22, wherein the locking mechanism further comprises acompression spring, and wherein the method further comprises: holdingthe locking mechanism in the steady state under a tension load less thana pre-determined tension load value.
 24. The method of claim 22, whereinthe locking mechanism further comprises a first link and a second link,wherein the semi-levered landing gear further comprises a positioningmechanism connected to a locking mechanism that secures an angle of thetruck beam in the toes up position, wherein a compression spring of thepositioning mechanism is connected to the first link, wherein thecompression spring is restrained in a pre-loaded position, and whereinthe method further comprises: compressing the locking mechanism beyondthe steady state; and the compression spring of the locking mechanismpreventing force from being applied to the second link.
 25. The methodof claim 22 further comprising a stop connected to the locking mechanismand wherein the method further comprises: The stop preventing rotationof the truck beam at a pre-determined degree of rotation in response toa change from the steady state to the locked state.